net/ipv4: defensive cipso option parsing

commit 076ed3da0c9b2f88d9157dbe7044a45641ae369e upstream.

commit 40413955ee26 ("Cipso: cipso_v4_optptr enter infinite loop") fixed
a possible infinite loop in the IP option parsing of CIPSO. The fix
assumes that ip_options_compile filtered out all zero length options and
that no other one-byte options beside IPOPT_END and IPOPT_NOOP exist.
While this assumption currently holds true, add explicit checks for zero
length and invalid length options to be safe for the future. Even though
ip_options_compile should have validated the options, the introduction of
new one-byte options can still confuse this code without the additional
checks.

Signed-off-by: Stefan Nuernberger <snu@amazon.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Simon Veith <sveith@amazon.de>
Cc: stable@vger.kernel.org
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 82178cc69c9618bae69c096290a7a96a8b8bade0..777fa3b7fb13d9f73a71eee2162ce472c1097b92 100644 (file)
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1512,7 +1512,7 @@ static int cipso_v4_parsetag_loc(const struct cipso_v4_doi *doi_def,
  *
  * Description:
  * Parse the packet's IP header looking for a CIPSO option.  Returns a pointer
- * to the start of the CIPSO option on success, NULL if one if not found.
+ * to the start of the CIPSO option on success, NULL if one is not found.
  *
  */
 unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
@@ -1522,10 +1522,8 @@ unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
        int optlen;
        int taglen;
 
-       for (optlen = iph->ihl*4 - sizeof(struct iphdr); optlen > 0; ) {
+       for (optlen = iph->ihl*4 - sizeof(struct iphdr); optlen > 1; ) {
                switch (optptr[0]) {
-               case IPOPT_CIPSO:
-                       return optptr;
                case IPOPT_END:
                        return NULL;
                case IPOPT_NOOP:
@@ -1534,6 +1532,11 @@ unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
                default:
                        taglen = optptr[1];
                }
+               if (!taglen || taglen > optlen)
+                       return NULL;
+               if (optptr[0] == IPOPT_CIPSO)
+                       return optptr;
+
                optlen -= taglen;
                optptr += taglen;
        }